With the recent progress in computer image-processing technology, a method has been developed comprising directly drawing an image on a photosensitive layer through light irradiation corresponding to digital signals, and a computer-to-plate (CTP) system has become common and comprises applying the method to a lithographic printing plate precursor to thereby directly draw an image in a photosensitive lithographic printing plate with no output through a silver salt mask film. The CTP system of a type that uses, as the light source for light irradiation, a high-power laser having a maximum intensity in a near-infrared or infrared region has some advantages in that high-resolution images can be formed through short-time exposure to light and photosensitive lithographic printing plates for use in the system can be handled in a daylight room. In particular, high-power and small-sized, solid-state lasers and semiconductor lasers capable of radiating infrared (IR) rays having a wavelength of from 760 nm to 1200 nm have become available.
As a lithographic printing plate precursors for CTP systems, those of a type having, on a substrate, a photosensitive layer that contains a thermoplastic substance such as thermoplastic resin and a photothermal conversion substance, in which the photothermal conversion substance converts laser light to heat during exposure to IR laser whereby the thermoplastic substance is thermally fused to form an image (see Patent Reference 1) have been proposed.
Others of a type having, on a substrate, a photosensitive layer that contains an unsaturated double bond-containing polymerizing substance and a photothermal conversion substance, in which the photothermal conversion substance converts laser light to heat during exposure to IR laser whereby the polymerizing substance is crosslinked to form an image (see Patent Reference 2) have been proposed.
In the lithographic printing plate precursors of those types, the exposed area forms an image and therefore, they require development for removing the non-exposed area. Different from conventional PS plates that require development with a strong alkaline developer, they may be developed with a neutral developer.
However, when a neutral developer is used, any not a strong alkaline developer, then the non-image area of a photosensitive layer can not always be removed satisfactorily and, as the case may be, there may occur a problem in that the non-image area may remain on the surface of the substrate and ink may adhere to it to cause staining of the non-image area.
Accordingly, a development system is desired which is capable of satisfactorily removing the non-image area of a photosensitive layer even in a case where a neutral developer is used for developing a lithographic printing plate precursor.
[Patent Reference 1] JP-A 9-131850
[Patent Reference 2] JP-A 2002-79772